Generally, oil dilution means that fuel component is diluted in oil in an oil pan of an engine, which reduces lubrication performance of the oil. In a case of a diesel engine, fuel is accumulated on an oil pan during a process of warming up for using a lean NOx trap (LNT) and a diesel particulate filter (DPF), and oil dilution occurs.
When the oil dilution in which the fuel is diluted in the oil in the oil pan excessively occurs, engine problems occur due to lubrication performance degradation.
A main reason for the oil dilution with fuel in the oil pan is an after-injection of the fuel for increasing temperature of LNT and DPF. When purifying exhaust using LNT and DPF, the exhaust gas cannot be purified without increasing temperature of LNT and DPF. Therefore, though the after-injection of the fuel is optimally controlled for suppressing the oil dilution, the oil dilution occurs.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.